Since the 1970s suction devices have been in use, in which the replaceable tip has been released and removed from the body with mechanical means without the need to touch the replaceable tip by hand. This is to avoid getting into contact with active and often even dangerous chemical and biological samples and reagents. The solutions have included mechanisms comprising levers or sleeves which have been mounted upon the pipette body. These mechanisms, which are known among others from the Finnish patent publications 56937 and 57540, have, however, increased the outer dimensions of the body beyond the outer diameter of the replaceable tip. From the U.S. Pat. No. 4,616,514 a suction device is known in which the replaceable tip is attached to the body the end part having finger-like strips provided with shoulders and in which the replaceable tip is released with a moveable means mounted within the end part acting on the finger-like strips. Also in this solution the end part will be greater than the replaceable tip to its diameter. In the development of diagnostic methods, nowadays one strives at such methods, in which the volumes of the samples and reagents utilized are increasingly smaller, which also leads to the use of increasingly smaller sample tubes. The removal means for replaceable tips mounted on the body of the suction device have restrained the changeover to using small sample tubes and therefore the removal devices have been removed from the suction devices. In these cases the tips have to be removed manually, whereby the risk for contamination again increases. There are also procedures in use in which the replaceable tip is removed by means of a U-shaped notch located in the side of a waste container.
In the following, the `suction device` stands for as such known manual or electrical suction devices or pipettes, which are used for pipetting, dispensing, diluting, titrating or mixing, or for a combination of all or some of these operations.
The use of these suction devices in handling liquids, such as samples or reagents, is described as a simplified example in the following. Once a replaceable tip has been attached to the end part of the body of the suction device and the piston moving in the cylindrical space of the end part is brought to its home position, whereby the piston is situated in the cylindrical space at that end which is closest to the end part of the suction device, the handling can be started. The outermost open end of the replaceable tip is immersed into the liquid of which it is desired to take a sample. When the piston is now moved inwards into the cylindrical space, the change in the volume formed jointly by the sample space of the replaceable tip and the cylindrical space brings about suction of the sample or reagent into the sample space of the replaceable tip. When it is desired to dispense the sample or the reagent taken in this way into the tip, the piston is moved towards the end part, whereby the said volume diminishes and at the same time the liquid in the replaceable tip exits from the open end of the replaceable tip. Several of these suction and dispensing stages can be combined in succession to bring about the desired handling. In these stages of sample handling the piston is moved to bring about the desired suction or dispensing. In most cases as the last stage the piston is moved past its home position mentioned above to a blowout position so that the replaceable tip is completely emptied. Thereafter the replaceable tip is removed from the end part of the body of the suction device.